FXUS62 KGSP 090838
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
338 AM EST WED DEC 9 2009
.SYNOPSIS...
A STRONG AREA OF LOW PRESSURE WILL MOVE INTO THE CENTRAL GREAT LAKES
STATES BY THIS EVENING. A COLD FRONT TRAILING THE LOW WILL SWEEP
ACROSS THE SOUTHERN APPALACHIANS TODAY. STRONG WINDS WILL ACCOMPANY
THE FRONT. ARCTIC HIGH PRESSURE WILL BUILD INTO THE REGION THURSDAY
AND FRIDAY. A SERIES OF WEAK UPPER LOWS WILL THEN KEEP THE WEATHER
UNSETTLED THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
70 KT 85H SSW JET TO CONTINUE TRANSLATING ENE ACRS THE CWFA THROUGH
MID-MORNING...ERODING SHALLOW WEDGE. ROUGHLY COINCIDENT IS THE
DOWNSTREAM TRANSLATION OF LLVL FRONTAL BAND MOISTURE AND THE
ASSOCIATED DIMINISHMENT OF WIDESPREAD SHOWERS.
PRIMARY CONCERN FOR TODAY IS THE MAGNITUDE OF THE UNIDIRECTIONAL
WESTERLY GRADIENT FLOW IN WAKE OF FROPA. WITH THE IMPINGEMENT OF
DEEP DRYING LAYER TODAY...CLEARING SKIES WILL PROMOTE RATHER DEEP
MIXING. THE 00 UTC NAM BUFKIT IS INDICATED AN INCREASE IN LLVL
CAPE AND GIVING THE POTENTIAL OF TAPPING 50-60 KT WIND GUSTS ATOP OF
THE MIXED LAYER DURING THE TIME OF MAXIMUM SFC PRESSURE
RISES...3-4MB/3 HR...AS PER LATEST NAM...ALL UNDERNEATH A VERY
ROBUST 100 KT 70H JET. GIVEN THE FACT THAT THIS STRONG WIND GUST
POTENTIAL IS IMMEDIATELY FOLLOWING A HEAVY RAIN EVENT...THE
POTENTIAL FOR AT LEAST SCATTERED UPROOTED TREES IS HIGH. BASED ON
THIS...HAVE UPGRADED HIGH WIND WATCH AREA TO A WARNING FOR
THE SAME VALID TIME.
UNDER FAIR SKIES...THE WELL MIXED ENVIRONMENT LINGERS INTO TONIGHT
SETTING US UP FOR A BLUSTERY AND SEASONABLY CHILLY NIGHT. A PERIOD
OF WESTERLY UPSLOPE COULD RESULT IN A FEW FLURRIES ACRS THE NW
NC MTNS.
&&
.SHORT TERM /THURSDAY THROUGH SATURDAY/...
AS OF 305 AM WEDNESDAY...MODIFIED ARCTIC HIGH PRESSURE WILL BUILD
INTO THE REGION ON THURSDAY. A LIGHT DOWNSLOPE COMPONENT TO THE
WINDS WILL HELP TEMPS RISE TO NEAR 50 OVER THE FOOTHILLS AND THE
L50S OVER THE PIEDMONT WHILE THE MTNS STRUGGLE TO REACH THE L40S IN
THE LOWER VALLEYS. THE AIRMASS WILL BE VERY DRY AND AFTERNOON
RELATIVE HUMIDITY VALUES WILL FALL TO BETWEEN 20 AND 25
PERCENT...AND POSSIBLY LOWER.
THE HIGH BE DIRECTLY OVER THE WESTERN CAROLINAS ON FRIDAY. THIS WILL
MAKE FOR A COLD FRIDAY MORNING WITH LOWS IN THE TEENS MTNS TO L-M20S
MOST EVERYWHERE ELSE. IT WILL BE A LITTLE WARMER IN SOME OF THE
THERMAL BELT AREAS OF THE UPSTATE. CONSIDERING THE ARCTIC NATURE OF
THE HIGH...THESE MIN TEMPS MAY PROVE A LITTLE ON THE HIGH SIDE. HIGH
CLOUDS WILL INCREASE DURING THE DAY ON FRIDAY...AND TEMPS WON/T MAKE
IT OUT OF THE 40S OVER THE FOOTHILLS AND PIEDMONT AND THE 30S IN THE
MTNS.
STRONGLY CONFLUENT UPPER TROPOSPHERIC FLOW WILL RESULT IN A 190+ KT
JET OVER THE MID ATLANTIC STATES FRIDAY. THE JET WILL BEGIN TO MOVE
OFF THE COAST ON SATURDAY...BUT THIS IS STILL GOOD FORCING FOR
MAINTAINING THE ANTICYCLONE OVER THE REGION. A COUPLE SRN STREAM
IMPULSES WILL MOVE ACROSS THE REGION FRI NIGHT AND SAT. THE MODELS
CONTINUE TO VARY ON THE TIMING AND AMOUNT OF QPF...AND THIS WILL
CONTINUE TO BE A LOW CONFIDENCE FORECAST. IT DOES MAKE SENSE THAT
WITH A STRONG HIGH...MOST OF THE PCPN WILL BE CONFINED TO THE DEEP
SOUTH AND COASTAL LOCATIONS. SO I THINK WE WILL MAINLY BE DEALING
ADVISORY CRITERIA WINTRY WX AT BEST ON SAT. AS FOR THE PCPN
TYPE...USING THE WX FROM NOMOGRAM TOOL...I GET A MIX OF
EVERYTHING...BUT WITH A TREND OF MORE SNOW EARLY IN THE DAY...AND
MORE OF AN ICY MIX LATER ON AND INTO THE NIGHTTIME HOURS.
&&
.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
AS OF 315 AM WEDNESDAY...A SECOND SRN STREAM SHORT WAVE WILL CROSS
THE REGION SOMETIME ON SUNDAY. WHEN DEALING WITH A FAST SOUTHERN
STREAM AND SUBTLE FEATURES THAT ARE STILL HALF WAY ACROSS THE
PACIFIC...TIMING IS IMPOSSIBLE. BUT...LOOKING AT THE LATEST EC AND
GFS...AT THIS TIME IT APPEARS THAT A SECOND ROUND OF FORCING MAY
RESULT IN PCPN OVER THE REGION DURING THE DAY. THIS BATCH MAY BE A
LITTLE FARTHER TO THE NORTH...THOUGH TEMPERATURES LOOK TO BE A
LITTLE WARMER THAN ON SATURDAY. THAT SAID...I/M KEEPING SUNDAY
DRY...ALBEIT CLOUDY...AS I DON/T WANT TO FLIP-FLOP ON THE FORECAST.
MONDAY LOOKS TO HAVE A BETTER CHANCE OF BEING A DRY DAY...THOUGH
THERE REMAINS A HINT OF COLD AIR DAMMING ACROSS THE REGION...AND WE
MAY NOT CLEAR UP. ANOTHER WAVE CROSSES THE REGION ON TUE-TUE NIGHT.
THE LATEST EC AND GFS ARE A LITTLE WEAKER WITH THE WAVE...BUT THEIR
TIMING IS FAIRLY SIMILAR. IT/S LOOKING MORE LIKE AN ALL RAIN EVENT
AS LLVL TEMPERATURES ARE MUCH WARMER THAN ON PREVIOUS RUNS. I/LL
KEEP A LITTLE MIX IN THE MTNS...BUT I WON/T EXPAND THE WINTRY PCPN.
&&
.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...NE WINDS AND IFR CIGS EXPECTED TO CONTINUE INTO
THE LATE NIGHT HOURS WITH AT LEAST OCNL VSBY RESTRICTIONS DUE TO
AREAS OF RAIN CONTINUING TO DEVELOP AND MOVE NE ACRS THE PIEDMONT.
STRONG LLVL JET TRANSLATING EAST ACRS THE FA WILL RESULT IN VERY
STRONG WIND GUSTS JUST ABOVE THE SFC. SFC FRONTAL BAND TO APPROACH
DURING THE PRE-DAWN HOURS AND WINDS EXPECTED TO SHIFT TO SW IN
RESPONSE. DRYING BEHIND THE COLD FRONT TO RAPIDLY DIMINISH RAINFALL
CVRG BY MID-MORNING...AS STRONG SW WIND GUSTS MIX DOWN TO THE SFC AND
LINGER INTO THE AFTERNOON.
ELSEWHERE ACRS THE FA...WIDESPREAD RAIN WILL LINGER ACRS THE
MOUNTAINS AND FTHLS INTO THE LATE HOURS BEFORE A PRE-DAWN COLD
FRONTAL APPROACH AND SUBSEQUENT PASSAGE CAUSES RAIN TO DIMINISH.
STRONG LLVL JET TRANSLATING EAST ACRS THE FA WILL RESULT IN VERY
STRONG WIND GUSTS JUST ABOVE THE SFC...WHICH WILL WORK DOWN TO THE
SFC LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON.
OUTLOOK...VFR EXPECTED TONIGHT THROUGH FRIDAY...ALTHOUGH GUSTY WINDS
MAY LINGER MUCH OF TUE NIGHT...ESPECIALLY ACRS THE MOUNTAINS. A GULF
COAST STORM SYSTEM COULD SPREAD LIGHT MIXED PRECIP INTO THE REGION
ON SATURDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR GAZ010-017-
018-026-028-029.
NC...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR NCZ033-
035>037-048>053-056>059-062>065-068>072-082-501>510.
SC...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR SCZ001>014-
019.
&&
$$
SYNOPSIS...MCAVOY
NEAR TERM...CSH
SHORT TERM...MCAVOY
LONG TERM...MCAVOY
AVIATION...CSH/JDL
